U.S. Pat. No. 5,712,609 ('609) to Mehregany et al., incorporated in its entirety by reference herein, describes a micro-mechanical condition sensor, fabricated on a silicon or bimetallic substrate, that is constructed and arranged for sensing a threshold value. As discussed in the '609 Patent, when an extreme temperature condition occurs and is sensed by a micro-mechanical temperature sensor, the sensor latches, and remains latched to provide a memory of the event available for detection purposes. Due to such characteristics, the micro-mechanical temperature sensing circuit has come to be known in the art as a maximum temperature memory switch (MTMS). For detection purposes, test ports are provided to permit the detection of the latched or unlatched states of the MTMS. The detection circuitry applied to the test ports typically detects an electrical condition of the latch, including a resistance, capacitance, continuity or other electrical condition.
In addition, to the foregoing, it is well-known in the art to combine one or more conventional sensors for measuring various temperatures and pressure conditions, with an integrated circuit (IC) to form a multi-chip module. A typical IC generally includes a suitable complimentary, metal-oxide semiconductor (CMOS) having a read only memory (ROM) circuit and an analog to digital (A/D) converter circuit. The IC is also typically constructed and arranged for converting analog temperature and pressure signals from the sensors to digital data corresponding thereto for storage in the ROM circuit of the CMOS chip.
For recording temperature and pressure conditions within pneumatic tires, the aforesaid multi-chip module has been incorporated into an electronic tire tag. A typical electronic tag includes a suitable radio frequency RF transponder having an antenna electrically connected thereto. In addition, the transponder includes one or more temperature or pressure sensors and an integrated circuit. Further, the integrated circuit has a serial number (SN) stored in the ROM circuit thereof, for identifying the electronic tire tag. Moreover, the integrated circuit includes suitable circuitry that is responsive to energization of the RF transponder from an external RF transceiver circuit, for causing the RF transponder to transmit data corresponding to the SN, followed by data corresponding the then current temperature or pressure conditions of the pneumatic tire.
Such electronic tire tags are conventionally encapsulated in rigid or semi-rigid materials, such as urethanes, epoxies or polystyrene resins, hard rubber compounds and the like. Thereafter, the encapsulated electronic tire tags have been wrapped with a green rubber material and, either incorporated within an uncured rubber tire or within a retread tire for vulcanization therewith to form an integral part of a cured or retreaded pneumatic tire, or separately vulcanized to form a cured rubber patch that may be fixedly attached to the innerliner of a pneumatic tire.
More recently, a MTMS as discussed in the '609 Patent, has been conventionally incorporated into an electronic tire tag. The MTMS provides an indication as to whether or not a predetermined, extreme threshold temperature has been experienced by the pneumatic tire in the course of usage thereof. Typically, the predetermined temperature has been selected to evaluate whether the warranties concerning the pneumatic tire will become void because the tire experiences the predetermined, extreme temperature. In effect, achieving the predetermined temperature can be considered irrefutable evidence of abusive use of the tire, i.e. operating the tire in an overloaded or underpressurized condition. However, the elevated temperatures and pressures achieved in the course of the vulcanization of tires, retreads or patches containing a MTMS have caused the latter switches to latch, indicating that the predetermined temperature has been reached. As a result, the MTMS has to be reset before it is useful for the intended purpose of providing an indication of abusive use of the tire in the course of operation thereof.